EPS vs Rock Wool vs PU: Panel Insulation Compared
Updated 2026-11-01 · JIUJIAN GLOBAL technical team
EPS is the cheapest with the lowest fire performance, rock wool is non-combustible and heavier with slightly worse thermal value per millimetre, and polyurethane gives the best thermal performance per thickness with a combustible core. For cold climates PU at 75-100 mm; for fire-sensitive or hot climates rock wool at 75-100 mm; EPS at 50-75 mm suits mild climates and temporary use.
Panel choice is usually made on price and then argued about at commissioning. The three cores differ in thermal value, fire behaviour, weight and cost, and the right answer depends on climate and code.
Comparison
| Property | EPS | Rock wool | Polyurethane (PU/PIR) |
|---|---|---|---|
| Thermal conductivity | 0.035-0.040 W/mK | 0.040-0.045 W/mK | 0.022-0.024 W/mK |
| Fire behaviour of core | Combustible, melts | Non-combustible | Combustible, chars |
| Typical panel thickness | 50-100 mm | 50-100 mm | 50-100 mm |
| Weight | Lightest | Heaviest | Light |
| Cost | Lowest | Higher | Highest |
| Best fit | Mild climates, temporary camps | Hot climates, fire-sensitive sites | Cold climates, energy-sensitive projects |
Choosing by climate
- Cold: PU at 75-100 mm, with attention to thermal bridging at the frame and the door threshold.
- Hot and dry: rock wool at 75 mm with a reflective roof coating; solar gain through the roof dominates.
- Hot and humid: rock wool or PU with a proper vapour strategy and sealed joints; condensation control matters more than the R-value.
- Mild and temporary: EPS at 50-75 mm is adequate and much cheaper.
The details that decide performance
A 100 mm panel with unsealed joints performs worse than a 75 mm panel with continuous gaskets. Check the tongue-and-groove detail, the corner flashing, the door and window interfaces, and the roof-to-wall junction. Thermal bridging through the steel frame is significant: a 0.6 mm steel web conducts far more than the panel core, which is why some specifications call for a thermal break strip.
What to ask the supplier
Panel test report with the fire classification of the assembly, thermal conductivity certificate for the specific foam density supplied, panel weight per square metre, and the jointing accessory list. Without the conductivity certificate, "PU panel" can mean a range of densities and performance levels.
Related: fire rating explained, load design, and the flat pack range.
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